Chapter 20 - Acids, Bases and pH

Question 1

What is a Brønsted-Lowry acid?

Answer 1

Proton donor (often +ve ion)

Question 2

What is a Brønsted-Lowry base?

Answer 2

Proton acceptor (often -ve ion)

Question 3

What is a conjugate-acid-base pair?

Answer 3

Contains two species that can be interconnected by transfer of a proton

Question 4

What is the formula and charge of a hydronium ion?

Answer 4

H₃O⁺

Question 5

What is a monobasic acid?

Answer 5

ONE hydrogen atom replaced in acid

Question 6

What is dibasic acid?

Answer 6

TWO hydrogen atoms replaced in acid

Question 7

What is tribasic acid?

Answer 7

THREE hydrogen atoms replaced in acid

Question 8

How to find the volume of base that will neutralise an acid depending on whether it is mono-, di-, or tri- basic?

Answer 8

Multiply known volume of acid by factors x1 or x2 or x3 (respectively)

Question 9

Formula to find out pH?

Answer 9

-log[H⁺]

Question 10

Formula to find out [H⁺]?

Answer 10

10^-pH

Question 11

Relationship between [H⁺] and [HA] for a STRONG ACID?

Answer 11

Due to complete dissociation the [H⁺] = [HA]

Question 12

Define a strong acid?

Answer 12

Completely dissociates into ions in an aqueous solution

Question 13

Define a weak acid?

Answer 13

Partially dissociates into ions in an aqueous solution

Question 14

What is the equation for K_a?

Answer 14

K_a = [H⁺] [A^-] / [HA]

Question 15

What does a larger K_a value mean?

Answer 15

• Equilibrium further towards products
• Greater dissociation
• Greater acid strength

Question 16

The stronger the acid the _______ the K_a value and the _______ the pK_a

Answer 16

Larger
Smaller

Question 17

The weaker the acid the _______ the K_a value and the _______ the pK_a

Answer 17

Smaller
Larger

Question 18

What do the further dissociations of weak dibasic and tribasic acids result in?

Answer 18

Latter dissociations being weak acids and pKa gets larger

Question 19

What are the two assumptions when calculating pH in weak acids?

Answer 19

1) [H⁺]_eqm = [A^-]_eqm (assumes dissociation of water is negligible)
2) [HA]_eqm = [HA]_start (assumes [HA] is > than [H⁺]_eqm)

Question 20

How can the K_a expression be simplified for WEAK ACIDS?

Answer 20

K_a = [H⁺]² / [HA]

Question 21

What is the equation, value and units of K_w?

Answer 21

K_w = [H⁺] [OH^-] = 1.00 x 10^-14 mol² dm^-6